I replaced the rear oil pan seal when I did my RMS. The oilpan still leaks, so I really suspect the RTV is just old and brittle.

you can replace that rear oilpan seal, but it's a little tricky. It wants to be installed with the oilpan clamping it down straight, but you would have to remove the engine to do that. I had to put the omega in bottom first then the top. I needed two pairs of vice grips to squeeze the omega down onto the oilpan seal so the bolts would line up. I used a lot of RTV around there, too.